1. Field of the Invention
The present invention generally relates to a controller for controlling the operational sequence of electrical loads and, more particularly, to a sequencing controller using electro-mechanical relays to control the operational sequence of multiple pumps in, for example, a septic system.
2. Description of the Prior Art
There are many applications for which it is desirable to sequence the operation of multiple electrical loads such as the sequential operation of multiple pumps used for an on-site septic system. In a simple septic system once waste water is ejected from a building it flows through the waste pipe and into a septic tank. Solids settle to the bottom of the tank to be broken down by an anaerobic process and clarified water effluent escapes the tank from an effluent pipe positioned opposite the waste pipe. The effluent is then channeled by a distribution box to various tubes fanned out below the surface of the ground in a drain field where it is allowed to leach slowly into the ground. For simple systems the entire system operates by gravity carrying the waste water from the building at the highest point to the drain field at the lowest point.
For systems which require waste water to move up hill at some point, a pump system is required to overcome the effects of gravity. In this situation, waste water is discharged into a pump chamber. When the water reaches a predetermined upper level, a float switch actuates a pump which continues to operate until the water is emptied to a predetermined lower level tripping another float switch. The amount of water pumped is referred to as the "dosing volume" and may be adjusted by changing the distance between the upper and lower levels where the pump switches on and off, respectively. If the pump fails to operate once the water reaches the upper level and the water continues to rise, a fail safe switch will be tripped sounding an alarm condition. If a redundant pump is available it may be activated at this time.
Complicated or larger systems, such as municipal systems, usually require more than one pump at a given location. Additional pumps may be provided simply for redundancy or to reduce the load on each individual pump and maintain even wear. For example if one pump is out of service, the remaining pump or pumps can maintain the load. Multiple pumps may also be required if the waste water is to be pumped to multiple destinations. Often in larger systems one drain field cannot leach enough water to support the entire system. Therefore, each time the pump chamber fills, pumps are rotated into and out of service in a round-robin fashion to pump the effluent to a different drain field. This rotating sequence occurs on each liquid level rise and fall cycle. The first pump in a given cycle sequence is referred to as the lead pump and the next pump in the sequence is referred to as the lag pump. As an added precaution, should the liquid level continue to rise even with the lead pump operating, a fail safe float switch may be provided causing the lag pump (presently idle) to energize and remain energized until the liquid level recedes sufficiently to de-energize both pumps.
Typically in such systems a pump selector switch is provided for each pump to allow manual or automatic control of the pump. However, when a given pump selector switch is placed in the off position (generally for maintenance purposes), the operation of the system is delayed until the liquid level reaches the fail safe float switch, causing the lag pump to activate. An additional and usually optional selector or circuit is required to cause the removed pump to be bypassed in the rotational sequence. Otherwise an interruption in operation will occur each time the given pump is called for but unavailable. This is obviously an undesirable situation. First, if the lag pump is not actuated until the liquid level rises above the fail safe float switch, the drain field to which the lag pump pumps may be overdosed by the extra liquid. This happening on a continual basis may cause flooding damage to the drain field. Further, typically an alarm is sounded when the liquid reaches the fail safe measure. Listening to and resetting this alarm each cycle would be annoying to the point where the operator may simply disable the alarm. In this situation, the pump system may continue to operate in its compromised condition causing damage to the system and possibly complete system failure.